The 'Sakamoto Days' novel is mainly about a former top - tier assassin named Sakamoto who has retired and become a fat, unassuming man. But his past catches up with him, and he gets dragged back into the dangerous world of assassins. It's full of action, interesting characters, and unique fight scenes.
The main character is Sakamoto, of course. He's the ex - assassin. And there are other assassins who play important roles as well, like Shin. They interact with Sakamoto in various ways, either as opponents or sometimes as reluctant allies.
I don't have enough information to say exactly who Miu Sakamoto is in this context. They could be an author, a storyteller, or someone involved in creating this 'never ending story'.
The manga ending of 'Haven't You Heard? I'm Sakamoto' was both conclusive and heartwarming. It gave a proper send-off to the characters and their adventures, leaving readers with a lasting impression.